课程名称︰有机化学三 课程性质︰五选三必修 课程教师︰陆天尧 开课学院：理学院 开课系所︰化学系 考试日期（年月日）︰2011/10/20 考试时限（分钟）：110 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题： Question 1 [15points] The energy of the gauche conformation(along C_2 and C_3 bond) of n-butane is 0.9 Kcal/mol higher than that of the anti-conformer. Based on this result, estimate the energy difference between cis- and trans-9-methyldecalines? Explane . Me Me ／＼▼／＼ ／＼▼／＼ │ │　 ││ │　 │ ＼／▲＼／ ＼／￥＼／ H H cis-decalin trans-decalin Assuming there is no difference in entropy and volume (under pressure) between these two compounds, estimate the free energy difference between these two isomers at 25℃ (gas constant R=1.987 cal/deg-mole Question 2 [10 points] Ruthenium carbene (ruthenium-carbon double bond) catalysts, known as the Grubbs catalysts, have been extensively used for the metathesis reaction. The Chauvin mechanism for the reaction is shown below: R Ph Ph R Ru=CHPh ╲__╱ __╱ ╲ ————→ ∣∣ ∣∣ ∥ ￣Ru ╱￣Ru R ↓ ↓ R § =C C=C-Ru =Ru C=C ╲ § ╲ Ph R Ph Some characteristic 1H NMR signals of the following compounds are shown below: Cl PCy3 H Cl PCy3 __OAc ﹨︱ ∕ ↖ ﹨︱ ∕ Ru== δ18.94(s) Ru== δ18.90(t) ∕︱ ﹨ ↙ ∕︱ ﹨ ↙ Cl PCy3 H Cl PCy3 H In the following metathesis reaction Cl PCy3 H Cl PCy3 __OAc Cl PCy3 H ﹨︱ ∕ 10 equiv.CH2CHCH2OAc ﹨︱ ∕ ﹨︱ ∕ Ru== ——————————→ Ru== + Ru== ∕︱ ﹨ 0℃ to RT ∕︱ ﹨ ∕︱ ﹨ Cl PCy3 Ph Cl PCy3 H Cl PCy3 H 10 mins major minor 2 hours minor major The triplet at δ18.90 appears on the spectrum in the first 10 minutes. However, whenthe reaction time is extended to 2 hours at room temperature, the triplet gradually diminishes and the singlet at δ18.94 becomes predominant, Explain this expermental observation. Question 3 [30 points] The mechanism for the formationof semicarbazones of substituted benzaldehydes at pH 6.5 is shown below: H+ H+ ↗ ↑ OH H O k_1 H ↖︳ H H H2N N ∥ → H2N N C k_2 H2N N ∕ ╲／ ╲NH ╱╲ ← ╲／ ╲N╱︳＼ → ╲／ ╲N=C ∥ ︳↘__↗ k_-1 ∥ ︱↗H Ar ∥ ︳ ﹨ O H O H O H Ar +H2O │ _ │ ∕ `~-_ │ ∕ `~_ 3+log k │ ∕ │ ∕ │ ∕ │ └───┴──── 0 σ A plot of the logarithm of the observed rate constant k against the Hammett substituent constants σ exhibits a non-linear correlation shown below. 1.Using steady state approach, show that k=k_1k_2/(k_-1+k_2) 2.Based on the mechanism above, please rationalize this observation. Question 4 [20 points] Two possible mechanisms for the ozonolysis of propone are considered. Mechanism 1-concerted mechanism: +︵ Ｏ=Ｏ Ｏ Ｏ -︱ ╱ ╲ ╱ ╲ Ｏ Ｏ Ｏ Ｏ Ｏ ↗ → ﹨___∕ → ﹨___∕ C== ╱ ╱ ╱ Me Me Me Mechanism 2-ionic mechanism: +︵ Ｏ=Ｏ Ｏ—Ｏ Ｏ -︱ ╲ ╱ ╲ Ｏ Ｏ Ｏ Ｏ ↘ ↗ → +___╱ → ﹨___∕ C== ╱ ╱ ╱ Me Me A kinetic isotope experiment is carried out and the results are shown below H(D) H(D) ╱ ╲ C==C C==C ╱ ╱ H3C H3C k_H/k_D 0.88 0.88 What do these isotope effects tell you about the mechanisms? Give your reasoning. Question 5 [25 points] Using the principle of the conservation of orbital symmetry (correlation diagram) and the molecular orbital diagrams for a three-memberd ring system and an allyl system shown below, explain why a cyclopropyl chloride undergoes disrotatory ring opening reaction under solvolytic conditions to give the corresponding allyl cation. On the other hand, an aziridine derivative gives the conrotatory ring opening product. Give your reasoning. ▼ ▽__△ ▽ ▲╲︳ __▲ ↗ ▼ ╲ ▽ 比较小 △ ▲ ▼ __△ ▼__ ╲︳ △╲︳ ▽ ▲ 比较大 ▼ ↘ ▼ __△ ▼__△ ╲ ▽ △╲︳ ▲ ▼ △ --

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